Improvements in Timeline: add "step forward" and "step backward" functions.

Conflicts:
	modules/DesktopTimeline/pom.xml
Improvements in Timeline: add "rewind to begin" and "rewind to end" functions.
Remove from Timeline concept of absolute/relative time.

There was idea of using absolute (double value) and relative (percentage
value) of timing during playback. But will be better to think more about
it.